Modulation indicating device



A ril 30, 1935. 9 ca. w. FYLER .v 1,999,872

MODULATION INDICATING DEVICE Filed March 14, 1934 InventoT: George W. Egler,

H is Attgrneg Patented Apr. 30, 1935 rA'rE rfo-rrics 1,999,872 MODULATION INDICATING DEVICE George W. Fyler, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application Mar-ch14, 1934, Serial No. 715,461

Claims.

indicating devices, or modulation alarms, and more particularlyto sucha device incorporating a a e us conduction device capable of passing 5 a large current in response to occurrence of predetermined percentages of. modulation.

An object of my invention is to providesuch a device which is capable of response at all times with equal accuracy and which is actuated only when the percentage of modulation is in excess or a predetermined value. r

.A further object of my invention is to provide such a modulation indicating device in whichthe accuracy of the reading or measurement of the percentage of modulation increases, as the percent modulationto be indicated increases, 7 V i The novel features which Ibelieve to be characteristic of myinvention are set forth with par.-

ticularity in the appended claims, My invention itself, however, both as to its organization and method of operation, together with further objects. and advantages thereof may best be understoodwith reference to the following description tak n in connection with the accompanying drawing in which Fig. 1 represents an embodiment of my invention, andFig. 2 represents a modification thereof.

Referring to Fig. 1 of the drawing, I, have indicated therein an antenna l and an inductance coil 2. These elementsmay comprise the output circuit 01 a transmitter in connection with which my invention is to be mpl y d- V The modulation alarm, or indicating device, in accordance with my invention, comprises a suitable electron discharge device 3, which is one of the gaseous conduction type having a plurality of electrodes surrounded by an attenuated gaseous medium, such as neon, argon, or mercury vapor. The anode circuit of this discharge device is supplied with operating potential from a uni directional source,;which maybe connectedto the conductors 4, and which is indicatedonthe drawing by plus and minus signs. The positive side of this source is connect-edthrough the contacts and winding of a relay 5 and limiting resistor 6 to the anode of the discharge device while the negative side is connected to ground. A potenti ometer is connected across this source and an intermediate point thereon is ,connectedto the cathode of the discharge device. The grid of the discharge device is connectedthrough a resistance 8, inductance 9,'and potentiometer it to the negative side of the source whereby both anode and bias potentials for the discharge device 3 are supplied from the source 4.

The discharge device 3 is controlled in response to theopercentage of modulation of the oscillations supplied to the antenna 5. I This is effected by means of a suitable rectifier circuit comprising the potentiometer l0 whereby aportion of the (Cl. 179-171) My invention relates to percentage modulation modulated oscillations in the transmitter output circuit are converted to a modulated unidirectional electroniotive force on resistance It. This rectifier circuit comprises a suitable unilaterally conducting discharge device ll having an anode circuit which is coupled by, means of a coupling coil i2 tothe inductance 2' ofthe transmitter output. This anode circuit also includes resistance l3, potentiometer i i; potentiometer l0,.-and, the

winding of a relay iii. The resistance I3 is of,

such a value that the external resistance of the rectifier circuit is many times greater than the internal resistance of the dischargedevice H. The relay ldcontrols the energizing :circuit of a suitable indicating device such as a neonlainp l6. During,normal' -operation' the current in the.

winding of relay i5 is sumcientto maintain'the armature of this relay iii-its: attracted position whereby the indicating device It is operated to o indicate the presence "of high ,irequency oscillations on the antenna l.

A meter ii is employed'both to indicate the bias voltage supplied to thegridof the discharge device ,3 and also the-percentage of modulation of the oscillations, suppliedfito the antenna l.

i This meteris provided withadouble throw switch 88, which whenin its leithand position, connects 1 themeter between ground andthe cathode of the discharge device thereby to indicate the bias upon the grid of-the discharge device 3. When in its righthand position it is connected across ,thatportion of potentiometer it which is included in the grid'circuit of the discharge. device 3, a suitable multiplier resistance E9; being ineluded inthc' circuit of; the meter. 7

The relay 5 is, of course, energized only :when the discharge device 3 passes current and then operates to interrupt the anode circuit of the discharge device. Thus this relay acts as a buzzer to interrupt the anodev circuit of the discharge device successively after the device becomesconducting. A series combination of resistance. 26 and capacitance 2!, is connected across the'contacts of'the relayrto eliminate sparking and in :shunttothis resistance is connected a suitable indicating device such ,as'aneon lamp, This lamp responds to the voltage induced in the coil ofrelay 5 due to deterioration of current there-. in when the contacts of the relay open and thus indicates the intervals when the. relay 5 is actuated, or when the discharge. device 3 is con ductive. V a

The gaseous conduction device 3, of course,

possesses the characteristic that no current flows, I

in the anode circuit thereof except when the voltage-- applied to the grid isless than a predetermined negative value. applied to the grid is less than thisvalue the device breaks, down and passes its full value. of anode current which is determined by the anode When the, voltage is voltage. When once broken down this anode current continues to flow as long as anode voltage is applied and irrespective of subsequent changes grid voltage.

The operation of my device as thus constructed may now be described. In adjusting the device. for operation the contact 21 on potentiometer may be moved to the lower extremity of the potentiometer so that no voltage due to rectified oscillations is supplied to. the grid. The contact 28 is then moved to a point on resistance 1' such that the vapor electric device is just conducting. The voltage supplied to the grid by the resistance 1 may then be indicated; upon the meter I! by moving the switch l8 to the left.

Let us assume that this negative voltage is, for I The contact 21 is now moved upward on potentiometer ID to such a point that example, 4 volts.

contact 28' may be-moved to reduce the bias indicated bythe meterto 3 volts without causing the discharge device to break down. The precaution of first moving the contact 21 upward before making this adjustment of contact 28 is taken'to avoid error due to anode current flowing in the lower portion of resistance '1 when the adjustment of contact 28 is made. Switch l8 may now be thrown to the right and the contact 21 adjusted to a point on resistance l0 such that the gaseous conduction device is conductive only when the-.volta ge on resistance in is at its extreme minimum value due to negative peaks of modulation. Let us suppose that the voltage sup- "percentage of modulation is thus indicated as only by modulation in excess of the predetermined 90%. Thus when so adjusted it will be apparent that the conduction device 3 becomes conductivewhenever the percentage of modulation exceeds 90%.

Hadcontact 28 been adjusted to supply a bias voltage of 3 volts-to the grid rather than 3 volts as in the previous case, other things being as described, it will be apparent that the device- 3 would become conductive only when the percentage modulation exceeds 95%. Thus the contacts 2 1 and 28 may be adjusted to cause the device 3 to become conductive, and the indicating device 26 to be actuated, only when the percentage modulation exceeds a suitable desired value. 7 7

It will be observed that since unidirectional potential is applied to the anode of the discharge device that the device'isin readiness at all times for response at any negativepeak of modulation in excess of a predetermined-percentage of modulation. The device'is actuated, however, only ,when the percentage of modulationis in excess of the predetermined value since the tube 3 is immediately rendered non-conductive by the device and is subsequently rendered conductive percentage.

It will be observed further that by use of the multiplier resistance I9 both the bias voltage supplied by resistance 1 and the modulated voltage supplied by resistance Hi may be indicated upon the same instrument 1! and with comparable accuracies. This device preferably is provided with two scales 29 and 30 one of which is uniformly calibrated throughout its length for indication of the voltages supplied by resistances land the other of which is progressively calibrated. That is, the spacing between the successive calibrations on the other scale progressively increases from one end of the scale to the other; This scale is employed when the switch [8 is in the righthand positionand indicates the percentage of modulation. The percentage of modulation is of course dependent upon the ratio of the difference between bias voltage supplied to the grid and the bias voltage necessary to' render the discharge device non-conductive to the average voltage supplied to the grid by the resistance it) when the device is just actuated on the negative peaks of modulation. The rate of change of this ratio progressively decreases with increase of the voltage on resistance Iflwith the result that the progressively calibrated scale may be employed thereby rendering possible greater accuracy of thereadings of the higher percentages of modulation. This is an extremely desirable characteristic of the apparatus since small changes in the percentage of modulation are more important at the higher percentages than is the case where the percentage of modulation is small. 1 v

The calibration of the: scale 30 is dependent upon a'certain fixed setting of the contact 28. With the contact in this fixed position the percentage of modulation of the oscillations supplied to the transmitter may be determined at any time by moving the contact 2'! downward to a point where lamp 26lights and then reading the percentage of modulation directly from the scale 33. If it be desired to utilize a difierent bias upon the discharge device 3 then a difierent scale 38, or suitable calibration chart may be employed. 1

To secure maximum accuracy of the apparatus the voltage chosen in the operation of the discharge device 3' should be such that the device always breaks down on the linear part of the grid-voltage anode-voltage breakdown characteristic. Since both the anode and grid bias voltages for discharge device 3 are obtained from the same source, variations in this source have little or no eiiect upon the accuracy of readings. By proper choice of the discharge device employed and the gas employed therein the effectsof tern perature variations are'also minimized or eliminated. H

A meter 3| is employedfor the purpose of indicating the amount of rectified current flowing in the circuit of discharge device ll. Choke coil 9 is provided to prevent the passage of high frequency oscillations from the coil 2 to the grid of the discharge device 3.

In Fig. 2 I have shown a modification of my invention to permit measurement of either the negative peaks or positive 7 peaks of modulation.

The equipment provided in accordance with this modification diiiers from that shown in Fig. l

. only in that a reversing switch 32is provided to value that the device 3 becomes conductive only on the positive peaks of modulation. For example, let us assume as before, that the discharge device becomes conductive when the negative voltage supplied to the grid is 4 volts or less and that the average voltage supplied by the resistance i is volts. Contact 28 may then be adjusted, for example, at such a point that the voltage supplied to the grid by resistance 1 is 23 volts. Since this voltage now is in opposed relation to that supplied by the resistance iii the average voltage on thegrid is minus .13. However, when the voltage on resistance I8 is 90% modulated or more the voltage upon the grid will be reduced to minus 4, or less, upon the positive peaks of modulation. Thus the lamp 2% will be lighted whenever the modulation ex-, ceeds 90%.

To ascertain an unknown percentage of modulation of the voltage on resistance N3 the contact 2? may be moved upward until lamp 26 lights at which instant the percentage modulation may be read directly from the scale 36 of the meter I1.

While I have shown'particular embodiments of my invention it will of course be understood that I do not wish to be limitedthereto since many difierent modifications may be made both in the circuit arrangement and in the instrumentalities employed, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention. V

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In combination, a gaseous conduction device having an anode, a cathode and a grid, said device being adapted to break down and pass current between its anode andcathode only when the potential applied to said grid isless than a predetermined negative Value, means to supply unidirectional voltages to said grid and anode of such values that said device is conductive, means to supply a modulated unidirectional voltage to said grid with such polarity as to render said conduction device non-conductive whereby said device becomes conductive only when the modulation of said unidirectional voltage exceeds a certain percent, means whereby the unidirectional voltage applied to said anode is repeatedly interrupted during the interval when said conduction device is conductive whereby said conductive device is conductive only during peaks of modulation, and means responsive to current in said anode operable only when said modulation peaks exceed acertain percentage modulation. p

2. In combination, a gaseous conduction device having an anode, a cathode and a grid, said device being adapted to break down and pass current between its anode and cathode only when the potential applied to said grid is less than a predetermined negative value, means to supply unidirectional voltages to said grid and anode of such values that said device is conductive, means to supply a modulated unidirectional voltage to said grid with such polarity as to render said conduction device non-conductive whereby said device becomes conductive only when the modulation of said unidirectional voltage exceeds a certain percent, a relay having its winding and contacts connected in series with said anode repeatedly to interrupt said anode circuit whenever said conduction device is conductive thereby to render said conduction device non-conductive after peaks of modulation exceeding said certain percentage of modulation have transpired, and

indicating means responsive to operation of said relay. v

3. In combination, a gaseous conduction device having an anode, a cathode and a grid, said device being adapted when anode operating voltage is applied thereto to change'from a nonconducting condition to a conducting condition at a certain value of grid voltage, means to supply a continuous unidirectional operatin voltage to saidanode, means to supply a bias voltage to said grid differing from said certain value thereby to maintain said device in one of said two conditions, means to supply a modulated unidirectional voltage to said grid in series with said bias voltage whereby said conduction device changes to the other of said two conditions only when the percentage of modulation of said modulated unidirectional voltage exceeds a predetermined value, and means whereby said conductive device is restored to said one condition after said percentage of modulation exceeding said predetermined value is reduced to a value less than said predetermined value.

4. In combination, a source of unidirectional voltage subject to Variation,a gaseous conduction device having an anode connected to the positive sideof said source, a grid connected to the negative side of said source, and a cathode connected 7 to an intermediate point on said source, means to maintain said connection to said anode when said conduction device is in non-conductive condition, and successively to interrupt 'said connection when said device is conductive condition, means to supply additional modulated unidirectional voltage to said grid, the percentage modulation of said additional voltage being such that said device changes from one of said conditions to the other and all of said voltages having values such that said conduction device changes condition in response to said modulation on a linear.

having an anode, a cathode and a grid, means .to supply continuous unidirectional anode operating voltage to'said devicewhen said device is.

in non-conducting condition and interrupted anode operating voltage to said device when said device is in conducting condition, means to supply a bias voltage'to'said device having a value such that said device is, in one of said conditionsnneans to supply an additional modulated unidirectional voltage to said grid, means to vary said last voltage to a value such that said devicechanges from said one condition to the other upon occurrence of modulation peaks, indicating means responsive to conduction of said'con duction device, a unidirectional voltage responsive indicating device having a scale progressively calibrated in terms of percentage of modulation, and means to connect said voltage responsive indicating device to indicate said modulated unidirectional voltage whereby for a given value oi said biasvoltage the percent of modulation of said modulated unidirectional voltage may be read directly from said scale and with increasing accuracy toward the higher percentages of modulation. i

GEORGE W. FYLER. 

